The objectives of this study are to examine the role of dopaminergic receptors on uterine and umbilical blood flows, maternal and fetal heart rates, arterial pressures, arterial blood gases and maintenance of fetal well-being. Pregnant Dorset sheep are operated on between 124-135 days gestation (term equals 145 days). Electromagnetic flow probes and catheters are placed on/in pertinent maternal and fetal vessels and chronic preparation is obtained. After a minimum of 96 hours to allow for recovery and reestablishment of maternal and fetal homeostasis, the test drug(s) are infused into a maternal or fetal vein. Physiologic measurements are then obtained utilizing the surgically placed flow probes and catheters.